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 A031396 Numbers k such that Pell equation x^2 - k*y^2 = -1 is soluble. 16
 1, 2, 5, 10, 13, 17, 26, 29, 37, 41, 50, 53, 58, 61, 65, 73, 74, 82, 85, 89, 97, 101, 106, 109, 113, 122, 125, 130, 137, 145, 149, 157, 170, 173, 181, 185, 193, 197, 202, 218, 226, 229, 233, 241, 250, 257, 265, 269, 274, 277, 281, 290, 293, 298 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Terms are divisible neither by 4 nor by a prime of the form 4*k + 3 (although these conditions are not sufficient - compare A031398). - Lekraj Beedassy, Aug 17 2005 REFERENCES Harvey Cohn, "Advanced Number Theory". LINKS Ray Chandler, Table of n, a(n) for n = 1..10000 (first 1000 terms from T. D. Noe) Hsin-Te Chiang, Mei-Ru Ciou, Chia-Ling Tsai, Yuh-Jenn Wu, Chiun-Chang Lee, On negative Pell equations: Solvability and unsolvability in integers, Notes on Number Theory and Discrete Mathematics (2018) Vol. 24, No. 3, 10-26. S. R. Finch, Class number theory [Cached copy, with permission of the author] D. Khurana and T. Y. Lam, Invertible commutators in matrix rings, J. Algebra and Applications, 10 (211), 51-71. K. Lakshmi, R. Someshwari, On The Negative Pell Equation y^2 = 72x^2 - 23, International Journal of Emerging Technologies in Engineering Research (IJETER), Volume 4, Issue 7, July (2016). Morris Newman, A note on an equation related to the Pell equation, The American Mathematical Monthly 84.5 (1977): 365-366. R. Suganya, D. Maheswari, On the Negative Pellian Equation y^2 = 110 * x^2 - 29, Journal of Mathematics and Informatics, Vol. 11 (2017), pp. 63-71. A. Vijayasankar, M. A. Gopalan, V. Krithika, On The Negative Pell Equation y^2 = 112 * x^2 - 7, International Journal of Engineering and Applied Sciences (IJEAS 2017), Vol. 4, Issue 7, 11-14. MATHEMATICA fQ[n_] := Solve[x^2 + 1 == n*y^2, {x, y}, Integers] != {}; Select[ Range@ 300, fQ] (* Robert G. Wilson v, Dec 19 2013 *) CROSSREFS Equals {1} U A003814. Cf. A031398, A002313, A133204, A130226 (values of x). See also A322781, A323271, A323272. Sequence in context: A020893 A281292 A145017 * A003814 A003654 A271787 Adjacent sequences:  A031393 A031394 A031395 * A031397 A031398 A031399 KEYWORD nonn AUTHOR STATUS approved

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Last modified March 24 11:49 EDT 2019. Contains 321448 sequences. (Running on oeis4.)